Things You'll Need:
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Step 1
Finish the lengths of trim ahead of time with paint, stain or varnish. The trim finish can either accent the finish of the stairs or match it.
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Step 2
Starting from the top step, measure the length of the inner corner between the top riser and the tread that meets it. If the tread is longer than the riser, take the measurement from the riser. Measure the next three stairs down as well, writing down each measurement. (The measurements should be very close to one another, but they may not be exact.)
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Step 3
Transfer the first measurement to a length of trim. Make a straight cut at the measurement with a miter saw. Remeasure for the next piece down, cut and repeat until you have three pieces in hand.
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Step 4
Lay the three pieces on your workbench. Drill pairs of holes in the face of the trim every 6 inches, with one hole of the pair going at an angle through the back of the trim and the other going through the bottom of the trim.
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Step 5
Affix all three pieces on their correct stairs with a hammer and trim nails, setting the heads of the nails with a nail set. Follow the angles of the two sets of pilot holes to nail the trim to the riser and the tread. Repeat the process for the next three steps down, continuing until the whole staircase is done.
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Step 6
If either side of the staircase is open so you can see the sharp, unfinished cut edge of the trim from the side, hand-sand the end of each piece to smooth out the wood and take the sharpness off the corner. Touch it up with whatever paint or finish you used on the rest of the piece.
